The European patent EP 1 093 039 B1 discloses a programmable field meter. A software-protection device is externally plugged to the field meter, the software-protection device allowing for an authorization check by means of a control unit of the field meter.
A particular disadvantage in this context is that additional space is required for the software-protection device. Moreover, the disclosed software-protection device is clearly visible from outside and may e.g. be stolen. In particular, an imitator will be able to recognize immediately that a software-protection device is provided.
A further disadvantage may particularly be that the disclosed software-protection device may be damaged during assembly or repair of the field meter as the disclosed software-protection device sticks out from the field meter.